1. Field of the Invention
The present invention relates to a magnetic head having a magnetoresistive element and a magnetic read-write device, as well as a magnetic memory.
2. Description of Related Art
In magnetic read-write devices, recording density has been improved remarkably. Magnetic read-write heads equipped in the magnetic read-write devices are required to have high performance for both of reading and writing characteristics.
Performance of the reading head can be enhanced by an anisotropic magnetoresistive (AMR) head for the recording density of 1 to 10 (Gb/in2) and by a giant magnetoresistive (GMR) head capable of attaining higher sensitivity for the recording density of 10 to 30 (Gb/in2). In the recording density of 20 to 70 (Gb/in2)at present, higher recording density of the writing head has been coped with by the advanced GMR effect referred to as specula GMR or NOL-GMR.
However, along with progress for further higher sensitivity, a writing system of higher sensitivity is required and it is considered that a tunnel magnetoresistive effect (TMR) will become predominant for the recording density of 70 to 150 (Gb/in2) and a GMR film (CPP-GMR: Current perpendicular to plane GMR) of flowing a detection current in the direction perpendicular to the film plane will become predominant for the higher recording density of 150 (Gb/in2) or more. Since existent GMR element adopts a system of flowing the detection current parallel with the film plane, it is referred to as CIP-GMR and distinguished from CPP-GMR. An example of the CPP-GMR system magnetic head structure is disclosed in Japanese Translation of Unexamined PCT appln. No. 509956/1999 and JP-A No. 221363/1995.
However, since the magnetic resistance change coefficient in the existent CPP-GMR element is too small, it involves a problem that the element can not be applied to an actual writing head. Where electric current is flown in the direction along the thickness of the CPR-GMR film, the current path is shorter and the resistance value of the element is smaller compared with a case of flowing the current in the direction along the film plane of the CPP-GMR film.
The resistance of CPP-GMR manufactured so far is about 0.1 to 0.5 mΩ for an element of 0.25 μm2 area. Further, since ΔR/R is about 20%, ΔR is 0.08 to 0.4 mΩ. It can be seen that the ΔR value is extremely small compared with an output value of 2 Ω or more required for application to the magnetic writing element.
The size of the CPP-GMR element may be made smaller for making the resistance R higher and ΔR greater but manufacture of the element area at present is limited to about 0.1 μm2. Further, since the resistance value is too small when the element area is decreased, it results in a problem of making measurement of the resistance R difficult.